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vacuum spark gap

Subject:   vacuum spark gap
  Date:   Sun, 20 Apr 1997 20:16:11 -0700
  From:   Gary Weaver <gweaver-at-earthlink-dot-net>
    To:   tesla-at-pupman-dot-com


BEST QUENCHING TEST

I bought a vacuum fan from American Science Surplus.  It has an AC/DC
motor.  The motor RPM's can be adjusted using a
variac.  I have found by increasing the fan motor RPM's the secondary
coil output increases also.  The secondary coil output
increase up to a point where the Tesla Coil peaks out to maximum
secondary coil spark output.  If the fan motor RPM is
increased beyond this point the spark output of the secondary coil
decreases.  Too much air flow is over quenching the spark
gap.

To prove the vacuum fan is over quenching the spark gap I did this
test.  I increased the fan RPM's beyond the point where
the tesla coil peaked out and produced the maximum length secondary coil
output.  At this increased setting the secondary
spark output became shorter.  With out changing the RPM setting I
reduced the gaps by 1 and the secondary coil output
returned to maximum length.  Too much air flow makes the spark gap act
like it has 1 gap to many and by reducing the number
of gaps by 1 it fixes the problem. 

I am using a Richard Quick spark gap with 8 gaps spaced .025 each.  The
copper tubes are 1" dia. x 2" long.  Using a 12K
30 ma neon to power the Tesla Coil and 4 of the 8 gaps I can adjust the
vacuum fan RPM's to find the spark gap maximum
quenching and peak out the secondary coil to maximum spark output.  If I
increase the power supply to 12K 60 ma I have to
use 6 of the 8 gaps, readjust coupling between the primary and secondary
coils and increase the RPM's of the vacuum fan to
find maximum quenching and peak out the secondary coil again.   If I
increase the power supply to 12K 90 ma I have to use
all 8 of the spark gaps and readjust the coupling between the primary
and secondary coils again and increase the RPM's of the
vacuum fan again to find maximum spark gap quenching.

Using a 12K 90 ma power supply, .0214 uf capacitor, Richard Quick
variable speed vacuum fan spark gap, 15 degree
wound primary coil with 1/4" tubing spaced 1/4" between tubes tapped at
turn 15.75, secondary coil 6.625" dia. x 23" long
close wound with #24 wire and a 10" thick x 27" diameter toroid made
with 4 galvinazed metal elbows.  I can get lots of 51"
long sparks from the toroid.  Maximum spark length so far is 66" long
from a 1080 watt power supply.


Gary Weaver